Why is everyone so different? How come some people
allergic to stuff while others aren’t? Is it that
some peoples DNA and molecules react to foods
and/or any kind of product differently than other
peoples' DNA?

Question Date: 2018-10-15

Answer 1:

A person’s individual characteristics are due
to both genetic factors (DNA) and environmental
factors.

Genetic factors are due to small
differences in the DNA between individuals.
This is called genetic variation and is
important for evolution because it provides
a diverse set of characteristics that can be
passed on through natural selection.

Everyone inherits their DNA (genes) from their
parents, and some traits are due solely to this
inherited DNA. These include genetic diseases
(Huntington’s disease or sickle cell anemia), eye
color, hair color, and skin color. Many other
traits are due to environmental factors such as
diet, hormones, or exposure to toxins. Even
identical twins -- who have the same genetic
make-up -- have different temperaments and
personalities, so genes do not specify everything.

Allergies are an interesting case where both
the environment and genetics are important. If
your parents are allergic to something, then it is
more likely that you will inherit the same
allergy, so there is a genetic component to
allergies. However, there is also an
environmental component to allergies that
is not well-understood. Human have evolved a
complex immune system that recognizes potentially
harmful agents like viruses and bacteria, and
eliminates them from the body. The immune
system learns to recognize a harmful substance
like a virus, and then it stores a “memory”
of this substance so that it can recognize it
later. In allergies, the immune system mistakenly
learns to recognize a normally harmless substance
like a peanut protein or a grass protein as a
harmful substance. When exposed to this harmless
substance, the immune system recognizes it as
harmful and launches an immune response to fight a
non-existent threat. There is a hypothesis that
not being exposed to enough germs and allergens as
a baby makes it harder for the immune system to
correctly learn what substances are OK and what
substances are harmful, leading to more allergies
in modern times as compared to the past, but no
one knows for sure why some people get allergies
and others do not. There is a lot of research
being done by scientists who work on the immune
system to figure out this mystery, and the answer
is probably a combination of genetics (DNA) and
environment.